A portable device, such as a cell phone, a recordable/reproducible digital camera or the like mount an acoustic component in order to emit sound outside and has a chassis with one hole or more in order to transmit sound emitted from the acoustic component. Such a portable device is vulnerable to water and dust. Therefore, as described in Patent document 1, in some conventional portable devices, a waterproof protection cover is disposed inside the holes and an acoustic component is disposed inside the waterproof protection cover.
FIG. 13 explains the disposition method of an acoustic component adopted in a conventional portable device. In FIG. 13, reference numerals 1301, 1302, 1303, 1304, 1305, 1306, 1307 and 1308 represent a chassis, a hole provided for the chassis 1302, a speaker being an acoustic component, packing, a waterproof protection cover, a double-sided tape for fixing the waterproof protection cover 1305 to the packing 1304, a double-sided tape for fixing the waterproof protection cover 1305 to the chassis 1301 and the vector of acoustic energy generated by the speaker 1303, respectively. A conventional portable device described in Patent document 1 adopts a waterproof protection cover having a gas-transparent characteristic of transmitting gas through it.
The vector 1308 of acoustic energy is troublesome in the neighborhood of the speaker 1303 that has generated the acoustic energy. For the waterproof protection cover 1305, a very thin one is adopted in order to suppress acoustic transmission loss. Therefore, as illustrated in FIG. 14, the troublesomeness of the vector 1308 easily generates a new vibration on the protection cover 1305 and when the vibration is generated, sound having a high frequency distortion component is emitted. Thus, in order to realize a preferable acoustic characteristic, it is indispensable to reduce the high frequency distortion component.
As such distortion countermeasures, a method of increasing a distance between the protection cover and the speaker in order to suppress the influence of the troublesomeness of the vector of the acoustic energy and/or to reduce the acoustic output of an acoustic component is adopted. Since part of sound that has transmitted through the protection cover is reflected by the chassis, it is usual to also increase a distance between the protection cover and the chassis. In FIG. 13, d3 and d4 indicate the distance between the protection cover 1305 and the chassis 1301 and the distance between the protection cover 1305 and (the vibration plate of) the speaker 1303, respectively.
It is necessary to emit the amount of sound sufficient for a user to clearly understand the content, which is not limited to a portable device. Thus, there is a limit in reducing the acoustic output. Therefore, conventionally, the distances d3 and d4 are increased. However, when the distances d3 and d4 are increased, naturally it becomes difficult to miniaturize and thin it. Therefore, in a portable device it is requested to dispose an acoustic component compactly while realizing a desirable acoustic characteristic.    Patent document 1: Japanese Laid-open Patent Publication No. H7-131375    Patent document 2: Japanese Laid-open Patent Publication No. 2003-503991    Patent document 3: Japanese Laid-open Patent Publication No.